You have two statements on one line without a semicolon separating them. You can't do that in Swift.
var highscore = 0 highscore = 99
Place the statements on separate lines.
var highscore = 0
highscore = 99
You could also simplify things by setting the value to 99 at the start.
var highscore = 99
I don't know if that's enough to fix the build error. You didn't show much code.
I recommend Hacking with Swift's 100 Days of SwiftUI free course to learn iOS development. They also have a forum where you can ask questions if you run into problems when going through the course. Their forum is more beginner friendly than this forum.
https://www.hackingwithswift.com/100/swiftui